The invention relates to a capacitive differential pressure sensor made using glass-silicon technology for industrial applications.
DE 42 07 949 discloses a capacitive differential pressure sensor made using glass-silicon technology in which a plate of silicon, serving as a pressure-sensitive diaphragm and as a first electrode, is arranged between two carrier plates consisting of glass, the plate and the carrier plate being integrally connected to one another in their edge region by anodic bonding in such a way that in each case a carrier plate combines with the plate serving as the diaphragm to form a measuring chamber, each carrier plate has a pressure supply duct, which runs perpendicular to the contact surfaces of the plate and of the carrier plates and via which the respective measuring chamber can be pressurized, and the surfaces of the carrier plates lying opposite the deflectable region of the plate serving as the diaphragm are each provided with a metallization, serving as a second electrode, in such a way that the first electrode and the second electrodes form a differential-pressure-dependent capacitor arrangement.
The differential-pressure-dependent deformation of the plate serving as a diaphragm brings about a change in capacitance of the capacitor arrangement, the change in capacitance being a direct measure of the differential pressure. The change in capacitance is measured electrically. The capacitor arrangement is connected to a measured-value processing device via connecting conductors.
With increasing miniaturization of such capacitive differential pressure sensors, the ratio of the measuring capacitances of the capacitor arrangement to the parasitic capacitances of the connecting conductors with respect to one another and with respect to reference potential deteriorates. As a consequence of this, the small change in capacitance xcex94CM/CM at the input of the measured-value processing device, with reference to the measuring capacitances CM and representing the measured value, occurs only as a change in capacitance xcex94CM/(CM +CS) with reference to the sum of the measuring capacitance CM and parasitic capacitances CS. As the ratio of the parasitic capacitances CS to the measuring capacitances CM increases, the resolution of the capacitive differential pressure sensor in a measuring range decreases.
In addition, production-related tolerances of the parasitic capacitances CS mean that a more complex procedure is required for calibrating the capacitive differential pressure sensor.
The invention is therefore based on the object of improving the ratio of the measuring capacitances to the parasitic capacitances in a capacitive differential pressure sensor of this type.
The invention proceeds from a known capacitive differential pressure sensor made using glass-silicon technology, in which a diaphragm plate of silicon, serving as a first electrode and with a pressure-sensitively deflectable region, is arranged between two carrier plates consisting of glass, the diaphragm plate and each carrier plate being integrally connected to one another in their edge region by anodic bonding in such a way that in each case a carrier plate combines with the diaphragm plate to form a measuring chamber, each carrier plate has a pressure supply duct, which runs perpendicular to the contact surfaces of the diaphragm plate and of the carrier plates and via which the respective measuring chamber can be pressurized, and the surfaces of the carrier plates lying opposite the deflectable region of the diaphragm plate are each provided with a metallization, serving as a second electrode, in such a way that the first electrode and the second electrodes form a differential-pressure-dependent capacitor arrangement. The capacitor arrangement is connected to a measured-value processing device.
The essence of the invention consists in that, outside the pressure-sensitively deflectable region, the diaphragm plate is the substrate of an electronic circuit which comprises at least one input stage of the measured-value processing device, which is connected to the capacitor arrangement and the output signal of which can be transmitted to the next-following stage of the measured-value processing device without any loss of information independently of line parameters.
The connecting conductors between the capacitor arrangement and the electronic circuit are so short in this case that the parasitic capacitances of the connecting conductors with respect to one another and with respect to reference potential are negligible in comparison with the measuring capacitance of the capacitor arrangement.
Apart from the second electrode of the measuring capacitance in each case, all the means for measured value acquisition are advantageously combined on a single component. This dispenses with the joining processes necessary in the case of a multi-part construction. In addition, production by the mask process known per se allows small tolerances of the mechanical parameters of the connecting conductors to be achieved, reducing the complexity of the procedure for calibrating the capacitive differential pressure sensor.
According to a further feature of the invention, the input stage of the measured-value processing device is a delta-sigma modulator. The output signal of the delta-sigma modulator is binary and can be transmitted to the next-following stage of the measured-value processing device without any loss of information independently of line parameters.
According to a further feature of the invention, the integration capacitor of the delta-sigma modulator is the capacitor arrangement of the capacitive differential pressure sensor. In this case, the differential pressure-dependent capacitance signal is digitized directly.
As a result, there is advantageously no longer any need for any tolerance-affected and potentially signal-falsifying analog preprocessing of the capacitance signal representing the measured value.